In recent years, further efficiency improvement and NOx reduction are being required of a gas turbine comprising a compressor, a combustor, a turbine, etc. by the regulations and social demands for environmental conservation. As a method for the efficiency improvement, in this type of gas turbines adopted is a method of increasing the temperature of the combustion gas existing from the combustor to the inlet of the turbine. However, there is a possibility that the amount of NOx emission increases with the increase in the temperature of the flame formed in the combustor.
Combustors designed to reduce the NOx emission include those employing premix combustion. The premix combustion is a combustion method in which air-fuel mixture obtained by previously mixing fuel and air together (premixed gas) is supplied to the combustor and brought into combustion. A combustor of this type comprises a burner having a premixer and a combustion chamber arranged downstream of the burner in the flow direction of the air-fuel mixture. The premixer is a device for generating the air-fuel mixture. The air-fuel mixture is supplied from the premixer to the combustion chamber and combusts in the combustion chamber. In the premix combustion, the fuel and air are previously mixed together and supplied to the combustion chamber, by which the temperature of the flame formed in the combustion chamber is uniformized and the NOx emission from the combustor is reduced. However, if the air temperature or the hydrogen content in the fuel increases, the combustion speed increases and the possibility of the so-called “flashback” (the flame formed in the combustion chamber flowing back to the premixer and so forth) arises. In consideration of the above-described situation, there has been proposed a combustor excelling in flashback resistance while also reducing the NOx emission (see Patent Literature 1, for example).